Boron nitride (BN) has become a very important industrial material in recent years due to a number of desirable properties. It can serve as a wide band gap semiconductor with high thermal conductivity and chemical inertness or as a thermal insulator. Boron nitride exists in several crystalline structures, including hexagonal and cubic. Boron nitride that has the cubic crystalline structure, commonly known as cubic boron nitride (or cBN), is of particular interest to the electronics industry. The structure of a boron nitride film may run from amorphous to polycrystalline to single crystal. A method for forming single crystal cBN is disclosed in Applicant's co-pending United States patent application Ser. No. 102,605, entitled, "AN IMPROVED METHOD OF FORMING CUBIC BORON NITRIDE FILMS," filed Aug. 5, 1993, the entire disclosure of which is incorporated herein by reference.
Cathodes are used in a number of electronic devices such as displays, power amplifiers and vacuum microelectronics. Conventional cathode structures are relatively low current devices which require either high extraction voltages or elevated temperatures for operation. Accordingly, it would be desirable to provide a cold cathode which would function at lower temperatures and voltages than existing cathodes.
Cubic boron nitride has been disclosed in the art as a material for use in microelectronics devices. For example, in U.S. Pat. No. 5,227,318, it is disclosed that p-type or n-type cBN can be used in the fabrication of bipolar transistors where the doped cBN forms the emitter and collector regions. Carbon doped cubic boron nitride films are disclosed in U.S. Pat. No. 5,330,561 wherein it is suggested that the films may be useful in high temperature electronics applications. Both p-type and n-type single crystal boron nitride is also disclosed in the afore-referenced U.S. Patent application Ser. No. 102,605. The use of diamond as a cold cathode is also known.
It is an object of the present invention to provide a cold cathode material which is capable of producing large currents at relatively low applied fields and at ambient temperature.
It is another object of the present invention to provide microelectronic devices having a cathode structure fabricated of boron nitride.
It is yet another object of the present invention to provide such cold cathode materials which can be fabricated by laser ablation, chemical vapor deposition or sputtering processes.